JP2944890B2 - Thermal air flow detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow detecting device which is suitably used for detecting an intake air flow rate of, for example, an automobile engine.

[0002]

2. Description of the Related Art In general, in an automobile engine or the like, a mixture of fuel and intake air is burned in a combustion chamber of an engine body, and the rotational output of the engine is obtained from the combustion pressure. Detecting the intake air flow rate is an important factor in calculating the above.

FIGS. 7 to 9 show a conventional thermal air flow detecting device.

[0004] In the drawing, reference numeral 1 denotes a thermal air flow detecting device provided in the middle of an intake pipe 2. The thermal air flow detecting device 1 is directed toward a combustion chamber (not shown) of an engine body. In order to detect the flow rate of the intake air flowing in the direction A shown in the drawing, it is provided in the middle of the intake pipe 2 via a mounting hole 2A.

[0005] Reference numeral 3 denotes a flow meter main body constituting a main body of the thermal type air flow detecting device 1, and the flow meter main body 3 is formed by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped cylindrical shape for winding a later-described reference resistor 14, and a substantially disk-shaped portion located on the base end side of the winding portion 4 and having terminal pins 8 A to 8 8D is provided integrally with the terminal portion 5 and extends in the radial direction of the intake pipe 2 from the distal end side of the winding section 4. It comprises a detection holder 6 to be positioned and a circuit casing 7 described below to which the terminal 5 is connected outside the intake pipe 2.

Reference numeral 7 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2. The circuit casing 7 is formed of an insulating resin material or the like, and has a bottom portion. On the side, a fitting portion 7A that fits into the mounting hole 2A of the intake pipe 2 is integrally provided. The circuit casing 7 has a flow rate adjusting resistor and a differential amplifier (both not shown) mounted on an insulating substrate made of, for example, a ceramic material, and incorporates them.

Reference numerals 8A, 8B, 8C, and 8D denote four terminal pins (generally referred to as terminal pins 8) projecting in the axial direction from the terminal portion 5 of the flowmeter main body 3, and each of the terminal pins 8 is a flowmeter. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding part 4 of the main body 3 and the detection holder 6 and is detachably connected to a connector part (not shown) of the circuit casing 7. Is what is done.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the flow meter main body 3 via the terminals 10A and 10B. The heating resistor 9 changes its resistance value in response to a temperature change. A platinum wire is wound around an insulating cylinder made of a ceramic material such as aluminum oxide (hereinafter, referred to as "alumina") or a platinum film is formed by depositing a platinum film. And a heating resistor element having a small diameter. The heat generating resistor 9 is heated by, for example, a temperature before and after 240 ° C. by energization from a battery (not shown), and is cooled by intake air flowing in the intake pipe 2 in the direction of arrow A. The resistance value changes in accordance with the flow rate of the intake air, and a flow rate detection signal is output.

Reference numeral 11 denotes a temperature compensation resistor provided on the detection holder 6 of the flowmeter main body 3 located on the upstream side of the heating resistor 9, and the temperature compensation resistor 11 is formed on an insulating substrate made of a ceramic material such as alumina. Is formed by depositing a platinum film using a means such as sputtering, and both ends of the platinum film are connected to the terminal 1 provided upright on the detection holder 6.
It is connected between 2A and 12B.

Reference numeral 13 denotes a protective cover mounted on the detection holder 6 of the flowmeter main body 3. The protective cover 13 is shown in FIG. 8 after the heating resistor 9 and the temperature compensation resistor 11 are mounted on the detection holder 6. As shown by the arrow, it is attached to the detection holder 6 to protect the heat generating resistor 9 and the temperature compensating resistor 11 and allow the flow of intake air. In FIG. 7, the heating cover 9 and the temperature compensation resistor 11 are shown in a state where the protective cover 13 is removed from the detection holder 6 in order to clearly show the resistance.

Further, reference numeral 14 denotes a reference resistance comprising a winding resistance wound around the winding part 4 of the flowmeter main body 3, and the reference resistance 14 has terminals at both ends thereof standing on the winding part 4. 15A and 15B, and connected in series to the heating resistor 9. Here, among the terminal pins 8, the terminal pin 8A is connected to the terminal 15A via the terminal plate, and the terminal pin 8B is connected to the terminal 15 via another terminal plate.
B, 10A. The terminal pin 8C is connected to the terminals 10B and 12B via another terminal plate, and the terminal pin 8D is connected to the terminal 12A via another terminal plate.

In the thermal air flow detecting device 1 of the prior art constructed as described above, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flow meter main body 3 is connected via each terminal pin 8. In a state of being connected to the connector portion of the circuit casing 7, the detection holder 6 and the like of the flowmeter main body 3 are inserted into the intake pipe 2 through the mounting hole 2A, and the suction pipe 2 is inserted into the mounting hole 2A.
By mounting the circuit casing 7 from the outer peripheral side of the above, the heating resistor 9 and the temperature compensating resistor 11 provided on the detection holder 6 are arranged at the center of the intake pipe 2.

In this case, by connecting the heating resistor 9 in series with the reference resistor 14 and connecting the temperature compensating resistor 11 in series with the flow rate adjusting resistor in the circuit casing 7, the heating resistor 9, the reference resistor 14, and the temperature A bridge circuit is composed of the compensation resistor 11 and the flow rate adjustment resistor, and the bridge circuit is energized from the outside so that the heating resistor 9 is 240 ° C.
Heat is generated at a later temperature.

In this state, when the intake air flows in the intake pipe 2 in the direction indicated by the arrow A toward the combustion chamber of the engine body, the flow of the intake air cools the heat generating resistor 9 and causes the heat generating resistor 9 to cool. Is detected, a detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage based on the voltage between both ends of the reference resistor 14 connected in series with the heating resistor 9, and the change in the output voltage is detected. Output to control unit not shown. Further, the control unit calculates the fuel injection amount and the like based on the output voltage.

[0015]

By the way, in the above-mentioned prior art, the resistance value of the heating resistor 9 is changed by utilizing the cooling of the heating resistor 9 by the flow of the intake air flowing through the intake pipe 2. Since the configuration is such that the intake air flow is detected based on the intake air flow, the heating resistor 9 is cooled by the intake air flow flowing in the direction indicated by arrow A (forward) in FIG. 7 and flows in the direction indicated by arrow B (reverse). It is also cooled by the air flow, and there is a problem that the air flow in the opposite direction erroneously detects the intake air flow rate.

That is, in an engine body having a multi-cylinder cylinder, the intake air is forced into each cylinder every time each intake valve (not shown) is opened as the piston reciprocates in each cylinder. Therefore, the flow velocity of the air flowing in the intake pipe 2 is repeatedly increased and decreased in accordance with the opening and closing of each intake valve as illustrated in FIG. 9 in the direction indicated by the arrow A (forward direction). become.

In particular, when the engine speed reaches from a low speed range to a middle speed range and the intake and exhaust volumes increase, the intake valve and the exhaust valve (not shown) overlap, and one of the exhaust The part may blow back into the intake pipe 2 with the opening of the intake valve, and at this time, the time t1, t shown in FIG.
The flow velocity becomes negative (minus) as shown in FIG. 2, and an airflow flowing in the direction of arrow B (reverse direction) is generated, which causes a problem that the intake air flow rate is erroneously detected.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can prevent erroneous detection of the intake air flow rate due to the reverse air flow, and can greatly improve the flow rate detection accuracy. It is another object of the present invention to provide a thermal air flow rate detection device in which a detection signal is made linear with respect to a flow rate.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a flowmeter main body having a base end attached to an intake pipe, and provided on the flowmeter main body located in the intake pipe. The present invention is applied to a thermal air flow detecting device having a heat generating resistor cooled by intake air flowing through the intake pipe.

A feature adopted by the invention of claim 1 is that a bridge circuit is formed including the heating resistor, and a change in the resistance value of the heating resistor forming the bridge circuit is determined by a flow rate detection signal corresponding to a flow rate. A first and a second flow rate detecting means which are provided before and after the heating resistor and whose resistance value changes in the flow direction of the intake air.
And a flow direction detecting means for detecting as a flow direction detection signal corresponding to the flow direction of the intake air based on a change in the resistance value of the first and second temperature sensitive resistances, and a flow from the flow direction detecting means. A sample and hold unit that uses a flow rate detection signal output from the flow rate detection unit based on a direction detection signal as a sample and hold signal, and a case where the flow of intake air is in the opposite direction based on the sample and hold signal from the sample and hold unit. Only, there is provided a signal inverting means for inverting the flow rate detection signal output from the flow rate detecting means.

According to the second aspect of the present invention, the heat generating resistor is formed on the insulating substrate attached to the flowmeter main body, and is formed in a film shape at least in a longitudinal direction of the insulating substrate. And the first and second temperature-sensitive resistors are respectively formed before and after the heat-generating resistor with respect to the flow direction of the intake air on the insulating substrate. 2 is constituted as a temperature-sensitive resistor.

[0022]

According to the first aspect of the present invention, the flow rate detecting means forms a bridge circuit including a heating resistor, and detects a flow rate corresponding to the flow rate based on a change in the resistance value of the heating resistor in the bridge circuit. The signal is taken out, and the flow direction detecting means outputs the flow direction of the intake air as a flow direction detection signal from the change in the resistance value of the first and second temperature-sensitive resistors. In the sample and hold means, a flow rate detection signal output from the flow rate detection means is output as a sample and hold signal based on the flow direction detection signal from the flow direction detection means, and the signal inversion means is used to output the signal from the sample and hold means. By inverting the flow rate detection signal output from the flow rate detection means based on the sample hold signal, the signal from the signal inversion means can be a signal indicating the flow rate and flow direction of the intake air flow rate.

According to the second aspect of the present invention, the first and second temperature-sensitive resistors formed on the insulating substrate in front of and behind the heating resistor with respect to the flow direction of the intake air are provided on the insulating substrate. Since the resistance value changes according to the flow direction of the air, when the first temperature-sensitive resistor has a smaller resistance value than the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the second temperature-sensitive resistor has a smaller resistance value than the first temperature-sensitive resistor, the flow of air can be detected as the reverse direction. Further, the heating resistor on the single insulating substrate,
Since the second temperature-sensitive resistor is formed as a film, the number of components can be reduced.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technology are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 21 denotes a thermal air flow detecting device according to the present embodiment, 22 denotes a flow meter main body which constitutes a main body of the thermal air flow detecting device 21, and the flow meter main body 22 is a conventional one. In substantially the same manner as the flowmeter body 3 described above, a winding portion 24 around which one reference resistor 23 having a resistance value R1 is wound, and a plurality of terminal pins (located on the base end side of the winding portion 24). (Not shown), and a detection holder 2 extending in the radial direction of the intake pipe 2 from the distal end of the winding part 24.
6 and a circuit casing 27 described later.

However, a slot (not shown) is formed in the flow meter main body 22 at the base end side of the detection holder 26 so that an insulating substrate 29 described later can be detachably attached thereto. As shown in the center of the intake pipe 2,
The heating resistor 30 and the like, which will be described later, are positioned via the insulating substrate 29. The detection holder 26 is provided with a protective cover (not shown) similar to the protective cover 13 described in the related art.

Reference numeral 27 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2. The circuit casing 27 is substantially the same as the circuit casing 7 described in the prior art. The mounting hole 2 of the intake pipe 2 is formed.
Although the circuit casing 27 has a fitting portion 27A that fits into the A, the circuit casing 27 is formed on an insulating substrate (not shown) made of, for example, a ceramic material, etc. These are built-in while mounted. 28A and 28B are terminals to which the windings of the reference resistor 23 are connected.

Reference numeral 29 denotes an insulating substrate mounted on the detection holder 26. As shown in FIG. 2, the insulating substrate 29 is made of an insulating material such as glass, alumina, or aluminum nitride and has a length of about 15 to 20 mm. It is formed in a rectangular flat plate having a width of about 3 to 7 mm. The base end of the insulating substrate 29 is a fixed end detachably attached to a slot of the detection holder 26, and the front end is a free end.

Reference numeral 30 denotes a heating resistor which forms a heating resistor formed on the insulating substrate 29. The heating resistor 30 has a resistance value obtained by depositing a platinum film by means such as printing or sputtering. RH. As shown in FIG. 2, the heating resistor 30 is located at an intermediate portion in the longitudinal direction of the insulating substrate 29 and extends in the width direction. The intermediate resistor portion 30A extends from both ends of the intermediate portion 30A in the length direction. The first and second extension resistance portions 30B and 30C extend in opposite directions.

Here, the heating resistor 30 has the intermediate resistor portion 30A and the extension resistor portions 30B and 30C as a whole having a crank shape, so that the heating resistor 30 and the first and second sense elements are formed on the insulating substrate 29. In addition to forming the heating resistors 31 and 32 compactly, the surface area (mounting area) of the heating resistor 30 is increased as much as possible, for example, so that the contact area with the intake air flowing through the intake pipe 2 can be increased. I have.

The current value of the heating resistor 30 is controlled by a current control transistor 38 described later.
It is heated so as to keep the temperature at a constant temperature (for example, about 240 ° C.).

Reference numerals 31 and 32 denote first and second temperature-sensitive resistors formed by depositing a temperature-sensitive material such as platinum on the insulating substrate 29 by means such as printing or sputtering. The first temperature-sensitive resistor 31 is formed so as to have a resistance value RT1 on the upstream side, and the second temperature-sensitive resistor 32 is formed so as to have a resistance value RT2 on the downstream side. A film is formed.

The first temperature-sensitive resistor 31 is located between the intermediate resistor 30A and the first extension resistor 30B of the heating resistor 30, and is parallel to the extension resistor 30B. It is formed in a rectangular shape so as to extend. The second temperature-sensitive resistor 32 is located between the intermediate resistor 30A and the second extension resistor 30C, and is formed in a rectangular shape so as to extend in parallel with the extension resistor 30C. The temperature sensitive resistors 31 and 32 are formed with a substantially uniform area on the insulating substrate 29. Normally, a current is applied from the sub power supply VS as shown in FIG. , The temperature-sensitive resistors 31, 32
Is effectively cooled by the flowing air, and the flow direction of the air can be detected with high sensitivity as a decrease in the resistance value.

Further, the first temperature-sensitive resistor 31 is located on the upstream side with respect to the forward flow of the intake air (the direction of arrow A), and the second temperature-sensitive resistor 32 is located on the downstream side. The heating resistor 30 is located between the temperature-sensitive resistors 31 and 32. Thereby, when the intake air flows in the forward direction indicated by arrow A, the first temperature-sensitive resistor 31 is cooled and the second temperature-sensitive resistor 31 is cooled.
When the temperature-sensitive resistor 32 receives heat from the heating resistor 30, the resistance value RT1 of the first temperature-sensitive resistor 31 decreases, and the resistance value RT2 of the second temperature-sensitive resistor 32 substantially decreases. Does not change.

On the other hand, when the flow of the intake air flowing in the intake pipe 2 is in the direction indicated by the arrow B in the opposite direction, the second temperature-sensitive resistor 32 is cooled, and the first temperature-sensitive resistor 31 is cooled. Receives the heat from the heating resistor 30, the resistance value RT2 of the second temperature sensing resistor 32 decreases, and the first temperature sensing resistor 3
The resistance value RT1 of 1 does not substantially change. As a result, the first
The resistance value RT1 of the temperature-sensitive resistor 31 and the second temperature-sensitive resistor 32
By comparing the resistance value RT2 with the resistance value RT2, it is determined whether the flow direction of the intake air is the forward direction or the reverse direction.

Reference numerals 33, 33,... Denote, for example, five electrodes formed at the base end side of the insulating substrate 29. The electrodes 33 are arranged in rows at a predetermined interval in the width direction of the insulating substrate 29. By inserting the base end side of the insulating substrate 29 into the slot of the detection holder 26, it is connected to each terminal (not shown) on the detection holder 26 side. Then, the heating resistor 3 formed on the insulating substrate 29 via each of the electrodes 33.
The zero, first, second temperature-sensitive resistors 31, 32, and the like are connected to each electronic component provided in the circuit casing 27, and constitute a processing circuit for flow rate detection shown in FIG.

Next, FIG. 3 shows a processing circuit for detecting a flow rate according to the present embodiment.

In FIG. 3, reference numeral 34 denotes one bridge circuit which constitutes a flow detecting means together with a differential amplifier circuit 37 described later. The bridge circuit 34 comprises a heating resistor 30, a temperature compensation resistor 35, and one reference resistor. 23 and a flow rate adjusting resistor 36 having a resistance value R2, and are configured as bridges in which the products of the resistance values of the opposing sides are equal. A connection point a between the heating resistor 30 and the temperature compensation resistor 35 is a current controlling transistor. The connection point b between the reference resistor 23 and the flow rate adjusting resistor 36 is connected to the ground.

In the bridge circuit 34, the heating resistor 30 and the reference resistor 23, and the temperature compensating resistor 35 and the flow rate adjusting resistor 36 are connected in series, respectively.
d is connected to the input terminal of the differential amplifier circuit 37, and a connection point c is connected to a sample-and-hold circuit 43 and an inversion circuit 4 described later.
4 is connected. The signal output from the differential amplifier circuit 35 becomes the current control voltage of the current control transistor 38 for controlling the applied current of the bridge circuit 34,
The output from the connection point c of the bridge circuit 34 is the reference resistance 2
3, the voltage becomes a flow detection voltage Va as a flow detection signal indicating the degree of cooling of the heating resistor 30 by the flow.

Here, the temperature compensation resistor 35 is provided on the detection holder 26 in the vicinity of the heating resistor 30.
The temperature compensation resistor 35 is not affected by the flow of the intake air, and the resistance value RK changes only depending on the temperature of the intake air.

In the bridge circuit 34 thus configured, when the bridge circuit 34 is in a balanced state, the current control voltage from the differential amplifier circuit 37 becomes zero,
From the connection point c, the voltage across both ends of the reference resistor 23 (flow detection voltage Va) in the equilibrium state is sampled and held.
3 and output to the inverting circuit 44. On the other hand, bridge circuit 3
4 is out of balance, that is, when the heating resistor 30 is cooled by the intake air, the resistance value RH of the heating resistor 30 is small. The current control voltage is output to the base of. Thereby, the current control transistor 3
8 is a circuit for controlling the current applied to the bridge circuit 34 to keep the cooled heating resistor 30 at a constant temperature.
Return 4 to equilibrium. At this time, the increased current value output from the connection point c of the bridge circuit 34 is equal to the reference resistance 23
, And is output to the sample and hold circuit 43 and the inversion circuit 44 as the flow detection voltage Va.

Here, as shown in the first row of FIG. 4, when the flow rate Q of the intake air fluctuates in the forward and reverse directions, the flow rate detection voltage Va as the flow rate detection signal shown in the second row becomes the reverse of the flow rate Q. When the flow is in the positive direction, the flow is in the forward direction again, and the flow detection voltage Va can detect the flow Q but cannot detect the flow direction. A point at which the flow rate detection voltage Va turns when the flow of the intake air changes from the forward direction to the reverse direction and from the reverse direction to the forward direction is defined as a return voltage value Va0.

Reference numeral 38 denotes a current control transistor. The current control transistor 38 has a collector connected to the battery voltage VB and a base connected to the differential amplifier 37.
And the emitter side is the bridge circuit 3
4 is connected to the connection point a. The current control transistor 38 controls the emitter current by changing the base current with the current control voltage from the differential amplifier circuit 37. As a result, the current control transistor 38 controls the current value applied to the bridge circuit 34, and performs feedback control for keeping the temperature of the heating resistor 30 at a constant temperature.

Next, reference numeral 39 denotes the other bridge circuit which constitutes the flow direction detecting means together with a comparison circuit 42 which will be described later, and the bridge circuit 39 comprises the first and second temperature-sensitive resistors 3.
1 and 32 and other reference resistances 40 and 41, which are configured as bridges in which the resistance values of the corresponding sides are equal. The connection point e of the first and second temperature sensitive resistors 31 and 32 is connected to the sub power supply VS (For example, 3V) and the reference resistance 4
The connection point f of 0, 41 is connected to the ground.

In the bridge circuit 39, the first temperature sensitive resistor 31 and the reference resistor 40 are connected in series, and the second temperature sensitive resistor 32 and the reference resistor 41 are connected in series.
h is connected to the input terminal of the comparison circuit 42,
The output terminal 2 is connected to an inverting circuit 44 via a sample and hold circuit 43. For this reason, when the bridge circuit 39 is in an equilibrium state, the flow rate Q of the intake air is zero, so that there is no difference between the resistance values of the temperature-sensitive resistors 31 and 32, and the resistance value is output via the comparison circuit 42. The flow direction detection voltage Vb as the flow direction detection signal has a voltage value of zero. On the other hand, when the balance of the bridge circuit 39 is lost, that is, when one of the temperature-sensitive resistors 31 and 32
Is changed from the connection point gh, the difference (RT1-RT2) of the resistance value is input to the comparison circuit 42 as a voltage, and the flow direction of the intake air is changed based on the difference between the resistance values. The signal (hereinafter, referred to as “flow direction detection voltage Vb”) is output to the sample and hold circuit 43.

Here, at the third stage in FIG.
Shows the relationship of the flow direction detection voltage Vb to the flow direction. When the flow direction of the intake air is the A direction (forward direction), the comparison circuit 42 outputs the flow direction detection voltage Vb having a predetermined voltage value Vb0.
b, and when the air flow direction changes from the A direction to the B direction (reverse direction), the comparison circuit 42 outputs a flow direction detection voltage Vb having a voltage value of zero.

Reference numeral 43 denotes a sample and hold circuit connected to the output side of the comparison circuit 42 as sample and hold means.
4 is modified based on the flow direction detection voltage Vb output from the comparison circuit 42. The sample hold voltage V shown in the fourth stage in FIG.
When the flow direction detection voltage Vb is the predetermined voltage value Vb0 as in c, the flow detection voltage Va is output as it is, and when the flow direction detection voltage Vb is zero, the flow detection voltage Va is output.
Is held at the return voltage value Va0, and this value is output.

Reference numeral 44 denotes an inverting circuit as signal inverting means. The inverting circuit 44 includes an operational amplifier 45, an input resistor 46 connected between an inverting terminal of the operational amplifier 45 and a connection point c of the bridge circuit 34, A feedback resistor 47 is connected between the inverting terminal and the output terminal of the operational amplifier 45. The output side of the sample and hold circuit 43 is connected to the non-inverting terminal of the operational amplifier 45.
6, 47 have the same resistance value. The inverting circuit 44 changes the waveform of the flow detection voltage Va output from the bridge circuit 34 based on the sample hold voltage Vc output from the sample hold circuit 43.

That is, as shown in the fifth stage of FIG. 4, when the flow of the intake air is in the positive direction, the flow detection voltage Va and the sample hold voltage Vc have the same waveform. Output as V0. On the other hand, when the flow of the intake air is in the reverse direction, the operation is performed with the amplification factor set to -1. Therefore, while the sample-hold voltage Vc is held at the return voltage value Va0, the output voltage V0 is the return voltage value of the flow detection voltage Va. It is output as a waveform inverted with respect to Va0. As a result, an output voltage V0 corresponding to the flow rate Q and flow direction of the intake air is output to a control unit (not shown).

The thermal air flow detecting device 21 according to this embodiment
Has the configuration as described above. Next, the operation of detecting the flow rate of the intake air will be described.

Here, when the flow of the intake air is in the direction of arrow A (forward direction), the first temperature-sensitive resistor 31 located on the upstream side of the insulating substrate 29 is cooled by the flow of the air. The second temperature-sensitive resistor 32 located on the downstream side receives the heat from the heating resistor 30. As a result, the balance is broken in the bridge circuit 39, and the flow direction detection voltage Vb which is positive (predetermined voltage value Vb0) is output from the comparison circuit 42.

In the bridge circuit 34, the heating resistor 30 is cooled by the flow of the intake air, and the cooling reduces the resistance value RH of the heating resistor 30, but the differential amplifier circuit 37 and the current control transistor 38 In order to keep the heating resistor 30 at a constant temperature, the value of the current applied to the bridge circuit 34 is increased, and this increased current value is detected by the reference resistor 23 as a voltage across the same. As a result, a positive flow detection voltage Va is output from the bridge circuit 34 to the inverting circuit 44.

Further, in the sample and hold circuit 43,
The flow detection voltage Va output from the comparison circuit 42 is deformed based on the flow direction detection voltage Vb, and the flow direction detection voltage Vb is a predetermined voltage value Vb0. Therefore, the flow detection voltage Va is used as the sample hold voltage Vc. Output.

Then, in the inverting circuit 44, the waveform of the flow detection voltage Va is deformed based on the sample hold voltage Vc, and there is no difference between the flow detection voltage Va and the sample hold voltage Vc. An output voltage V0 corresponding to the flow rate and the positive flow direction is output to a control unit (not shown).

On the other hand, the air flow is in the direction of arrow B (reverse direction).
In the case of (2), the second
Is cooled by this flow of air,
The first temperature-sensitive resistor 31 located on the upstream side is the heating resistor 3
Receives heat from zero. As a result, the balance of the bridge circuit 39 is broken, and the comparison circuit 42 outputs a reverse flow detection voltage Vb having a voltage value of zero.

In the bridge circuit 34, the heating resistor 30 is cooled by the flow of the intake air in the reverse direction, and a positive flow detection voltage Va is output to the inverting circuit 44 by the cooling.

Further, in the sample and hold circuit 43,
The waveform of the flow detection voltage Va output from the comparison circuit 42 is deformed based on the flow direction detection voltage Vb, and since the flow direction detection voltage Vb is zero, the return voltage Va0 of the flow detection voltage Va is used as the sample hold voltage. Output as Vc.

Then, in the inverting circuit 44, the waveform of the flow detection voltage Va is deformed based on the sample hold voltage Vc, and the sample hold voltage Vc is the return voltage value Va0. Therefore, the flow detection voltage Va is converted to the return voltage value Va0. , And output as the output voltage V0.

As a result, even when the flow direction of the flow rate Q fluctuates in the forward and reverse directions, the output voltage V0 output from the inverting circuit 44 can be changed as shown in the fifth stage of FIG. It can be accurately and continuously detected.

Thus, in the thermal air flow detecting device 21 according to the present embodiment, the heating resistor 30 is formed on the insulating substrate 29, and the first and second heating resistors 30 are located before and after the heating resistor 30. Since the second temperature-sensitive resistors 31 and 32 are formed, the number of components can be reduced, and the direction of air flow can be detected by the first and second temperature-sensitive resistors 31 and 32. The flow rate of the intake air can be detected from the change in the resistance value of the heating resistor 30.

The change in the resistance value of the heating resistor 30 of the one bridge circuit 34 due to the flow rate Q is output to the inverting circuit 44 as the flow rate detection voltage Va, and the first and second temperature sensing elements of the other bridge circuit 39 are also output. The change in the resistance value of the resistors 31 and 32 according to the flow rate Q is output as a flow direction detection voltage Vb which becomes positive or negative with respect to the flow direction via a comparison circuit 42.
The sample and hold circuit 43 deforms the flow rate detection voltage Va based on the flow direction detection voltage Vb, and outputs the flow rate detection voltage Va as it is when the flow is in the forward direction, and outputs the flow rate detection voltage Va when the flow is in the reverse direction. Is output to the inverting circuit 44 as the sample-and-hold voltage Vc. The inversion circuit 44 deforms the waveform of the flow detection voltage Va based on the sample hold voltage Vc, outputs the flow detection voltage Va as it is as the output voltage V0 when the flow is in the forward direction, and outputs the flow rate voltage as the output voltage V0 when the flow is in the reverse direction. The detection voltage Va can be output as a voltage inverted by the return voltage value Va0. As a result, the output voltage V0 output from the inverting circuit 44 can be a voltage indicating the flow direction and the flow rate of the flow rate Q, and the flow rate Q of the intake air can be continuously detected with high accuracy. .

Further, the first and second temperature-sensitive resistors 3
Because 1, 32 is heated by the sub power supply VS,
The resistance values RT1 and RT2 of the temperature-sensitive resistors 31 and 32 can be sensitively changed by the cooling effect of the air flow, and the flow direction of the air can be detected with high sensitivity.

As a result, the control unit can perform accurate engine control by performing air-fuel ratio control, ignition timing control, injection amount control, etc. based on the averaged flow rate Q.

In the above embodiment, the temperature compensation resistor 35
Has been described as being provided near the detection holder 26,
The present invention is not limited to this. As shown in a first modified example of FIG. 5, a slit S is formed in the insulating substrate 29 'from the distal end side to the proximal end side so that the first substrate portion 29A' 2 substrate part 2
9B ', a heating resistor 30 and first and second temperature-sensitive resistors 31, 32 are formed on the first substrate portion 29A', and a temperature is formed on the second substrate portion 29B '. The compensation resistor 35 is formed in a film shape. As a result, the heating resistor 30, the first and second temperature-sensitive resistors 31, 32, and the temperature compensating resistor 35 can be formed on the insulating substrate 29 ', and the number of components can be greatly reduced.

In the above embodiment, the heating resistor 30 formed on the insulating substrate 29 and the first and second temperature-sensitive resistors 3 are formed.
2 are formed as shown in FIG. 2, but the present invention is not limited to this, and as in a second modification shown in FIG.
52, 53 extending from the distal side to the proximal side of the
Is formed, and the insulating substrate 51 is formed by the slits 52 and 53.
Are divided into first, second, and third substrate portions 51A, 51B, and 51C, and the first, second, and third substrate portions 51A, 51B, and 5C are separated.
Heating resistor 54 and first temperature-sensitive resistor 5 are respectively provided on 1C.
5. The second temperature-sensitive resistor 56 may be formed as a film. In this case, it is desirable that the first substrate portion 51A has a relatively large surface area than the other substrate portions 51B and 51C. Further, in the case of this modification, the slit 5
Since the resistors 54, 55, and 56 are separated by 2 and 53, it is possible to reduce the influence of the heat of the heating resistor 54 on the resistors 55 and 56 via the insulating substrate 51. Furthermore, the temperature compensation resistor 35 may be integrally formed as shown by a two-dot chain line.

Further, in the above embodiment, the flowmeter main body 22
Although it has been described that one reference resistor 23 wound around the winding portion 24 is provided to protrude into the intake pipe 2, the present invention is not limited to this. The reference resistor 23 may be provided together with the flow rate adjusting resistor 36 and the like.

Further, in the above embodiment, the bridge circuit 34 constituting the flow detecting means is formed by the heating resistor 30, the temperature compensating resistor 35, the reference resistor 23 and the flow regulating resistor 36. However, the bridge circuit 34 may be formed by using a fixed resistor instead of the temperature compensation resistor 35 and the flow rate adjustment resistor 36.

[0068]

As described above in detail, according to the first aspect of the present invention, the flow rate detecting means forms a bridge circuit including a heating resistor, and a change in the resistance value of the heating resistor in the bridge circuit is used as a flow rate detection signal. Take-out and flow direction detecting means,
A flow direction detection signal corresponding to the flow rate of the intake air by forming a bridge circuit from the second temperature-sensitive resistor and the reference resistor, wherein the balance of the bridge circuit is broken by a change in the resistance value of the first and second temperature-sensitive resistors. Is output. The sample-and-hold means transforms the flow rate detection signal into a sample-and-hold signal based on the flow direction detection signal. By inverting the signal, the flow direction and the flow rate of the intake air can be detected by the signal from the signal inversion means.

As a result, erroneous detection due to fluctuations in the output voltage in the forward and reverse directions of the flow rate can be prevented, the intake air flow rate can be detected with high accuracy, and the air-fuel ratio control and the like can be effectively performed.

According to the second aspect of the present invention, the first and second temperature-sensitive resistors formed on the insulating substrate in front of and behind the heating resistor with respect to the flow direction of the intake air are provided on the insulating substrate. Since the resistance value changes according to the flow direction of the air, when the first temperature-sensitive resistor has a smaller resistance value than the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the resistance value of the second temperature-sensitive resistor is smaller than that of the first temperature-sensitive resistor, the flow of air can be detected as the reverse direction, and the resistance values of the heating resistor and the first and second temperature-sensitive resistors can be detected. Can be sensitively changed by the air flow, and the flow direction can be accurately detected. Furthermore, since the heating resistor and the first and second temperature-sensitive resistors are formed on a single insulating substrate, the number of components can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state in which a thermal air flow detecting device according to an embodiment is attached to an intake pipe.

FIG. 2 is a plan view showing a heating resistor and first and second temperature-sensitive resistors formed on an insulating substrate.

FIG. 3 is a circuit diagram showing a circuit configuration of the thermal air flow detecting device according to the embodiment.

FIG. 4 is a characteristic diagram showing a voltage from each circuit with respect to a flow rate Q according to the embodiment.

FIG. 5 is a plan view showing a heating resistor, first and second temperature-sensitive resistors, and a temperature compensation resistor formed on an insulating substrate according to a first modified example.

FIG. 6 is a plan view showing a heating resistor and first and second temperature-sensitive resistors formed on an insulating substrate according to a second modification.

FIG. 7 is a longitudinal sectional view showing a state in which a thermal air flow detecting device according to a conventional technique is attached to an intake pipe.

FIG. 8 is a perspective view showing a flow meter body, a heating resistor, and the like according to a conventional technique.

FIG. 9 is a characteristic diagram showing fluctuations in the flow velocity of intake air.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Thermal air flow detector 22 Flowmeter main body 23 Reference resistance 29, 29 ', 51 Insulating substrate 30, 54 Heating resistor 31, 55 First temperature-sensitive resistor 32, 56 Second temperature-sensitive resistor 34 Bridge Circuit (flow rate detecting means) 35 Temperature compensation resistor 36 Flow rate adjusting resistor 37 Differential amplifier circuit 39 Bridge circuit (flow direction detecting means) 42 Comparison circuit 43 Sample hold circuit (sample hold means) 44 Inverting circuit (signal inverting means)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-29017 (JP, A) JP-A-6-265385 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G01F 1/68 F02D 35/00 G01P 5/12

Claims (2)

(57) [Claims] 1. A flowmeter main body having a base end attached to an intake pipe and a flowmeter main body located in the intake pipe and provided on the flowmeter main body.
A thermal air flow rate detection device comprising: a heating resistor cooled by intake air flowing through the intake pipe; a bridge circuit including the heating resistor; and a resistance value of the heating resistor forming the bridge circuit. Flow rate detecting means for outputting a change in the flow rate as a flow rate detection signal corresponding to the flow rate, and first and second means which are provided before and after the heating resistor and have a resistance value that changes in the flow direction of the intake air. And a flow direction detecting means for detecting as a flow direction detection signal corresponding to the flow direction of the intake air based on a change in the resistance value of the first and second temperature sensitive resistances, and a flow from the flow direction detecting means. Sample and hold means for transforming the flow rate detection signal output from the flow rate detection means into a sample and hold signal based on the direction detection signal; Only when the flow of intake air based on a field signal of the reverse, the flow signal to invert the flow rate detection signal outputted from the detection means reversing means and the thermal air flow detecting device, characterized in that the provided. 2. The heat-generating resistor is formed as a heat-generating resistor formed on an insulating substrate attached to the flowmeter main body and extending in a film shape at least in a longitudinal direction of the insulating substrate. The first and second temperature-sensitive resistors are formed as film-formed first and second temperature-sensitive resistors separated from each other before and after the heating resistor with respect to the flow direction of the intake air on the insulating substrate. The thermal air flow detecting device according to claim 1, wherein the thermal air flow detecting device is constituted.